This invention relates generally to the art of carburetors and more specifically to carburetors having by-pass air passageways for by-passing throttle valves thereof.
Public policy is increasingly requiring that new automotive vehicles be equipped with apparatus for controlling the emissions of noxious fumes from exhaust systems of such vehicles. In this regard, it is generally well known that running automotive vehicles at excessively rich mixtures produces more unburned carbons than is generally desired. In the past, carburetor idle circuits have often been among the worst offenders of providing excessively rich mixtures because mechanics have employed rich mixtures in order to make engines idle smoothly. In this respect, one reason it is difficult to obtain a smooth idle is that decreased air flow results in uneven distribution of idle fuel charges.
Engineers have employed several methods to overcome this uneven distribution problem. For example, they have increased idling speeds so as to get greater air flow and increased engine temperatures to improve vaporization.
Some manufacturers have drilled air bleed holes in throttle plates so as to increase air flow and thereby deliver more uniform distributions of fuel/air mixtures to combustion chambers. However, the sizes and placements of such throttle plate holes have been extremely critical to their effectiveness. Some manufacturers have included by-pass idle air systems in their throttle flanges for by-passing air around throttle valves. In such cases air is taken from above the throttle valves through passages and discharged into bores below the throttle valves. Some of these air by-pass systems have discharge ports adjacent to the idle-circuit fuel-discharge ports and some share discharge ports with the idle circuit, for example, see U.S. Pat. No. 2,763,285 to Reeves.
A difficulty which is sometimes encountered when employing a supplementary air by-pass circuit is that, because modern automotive vehicles idle at such fast speeds, when their ignition switches are turned off they often continue to run due to a "dieseling" action. Thus, it is an object of this invention to provide a supplementary by-pass air circuit which tends to prevent "dieseling" when an engine is turned off.
Another difficulty with some prior art air by-pass circuits is that the orientation and locations of discharge ports thereof have been extremely critical, thus, making them difficult and expensive to manufacture. Therefore, it is an object of this invention to provide a supplementary air by-pass system in which the orientation and location of a discharge port is not as critical as in prior art devices.
Still another difficulty with some prior art supplementary air by-pass circuits is that they were unduly difficult to manufacture because they do not allow easy adjustment to produce optimum desirable fuel/air mixtures. Therefore, it is yet another object of this invention to provide a supplementary air by-pass system which allows easy fuel/air mixture adjustment after manufacture.
It is still another object of this invention to provide a supplementary air by-pass system which is relatively inexpensive to manufacture and not unduly complex in structure.